This invention relates in general to motion devices, and in particular, to motion devices that employ shape memory material.
Certain materials are known to have the property of returning to a preset shape from a deformed shaped upon heating or upon application of electrical stimulation. Such materials are commonly referred to as having shape memory in recognition of this memory effect. Shape memory materials are available with a wide variety of properties, and construction parameters can be manipulated to vary factors such as the preset shape, the force exhibited by the material when returning to its preset shape, the force required to deform the material from its preset shape, the transition temperature, and the like.
The prior art describes a variety of ways to utilize the transducer properties of shape memory materials in the construction of devices such as motors, actuators, solenoids, and other mechanisms requiring mechanical motion. Generally, such applications employ an external force such as a spring, cantilever member, or the like, to deform the shape memory material from its preset shape, and heat or electrical stimulus to return the material to its predeformed state.
A shape memory alloy application is described in U.S. Pat. No. 543,678 issued to Hoiberg on Aug. 6, 1996, entitled FLAT MOTORS, in which a shape memory actuator wire is used to deflect a resilient cantilever arm that drives mechanical operation of the motor. Here, the shape memory actuator wire is heated through stimulation by an electrical pulse, and contracts to its memory shape, thereby pulling the cantilever arm to a particular position. When stimulation ceases, the actuator wire cools, such as by ambient air cooling, and the resilient lever arm acts to deform, or stretch, the actuator wire. In another application described in U.S. Pat. No. 5,55,328, issued to Hall et al. on Sep. 6, 1996 for an AUTOMATICALLY DEPLOYABLE AND RETRACTABLE COMBINER MECHANISM, a combination of a conventional spring and a shape memory alloy spring is used to detract and deploy a combiner attached to a helmet. A more complex system is described in U.S. Pat. No. 5,316,979 issued to Schwatz, Jr. on Apr. 26, 1994 for a MULTIPLEXING INCREMENTAL LINEAR ACTUATOR SYSTEM, in which multiple shrinkable wires provide incremental linear movement, and a return spring provides a countervailing force.
Linear servo mechanisms are known in which precise mechanical movements are effectuated by using an electro-mechanical device, such as an electrical motor, and feedback systems to ensure precise positioning of elements. However, linear servo control is typically performed by solenoids, screw motors and pneumatics, and often have elaborate construction. As the requirement grows for more miniaturized mechanical devices, there is a need to have linear servo devices having simple construction with the minimum number of moving parts.
Shape memory transducers have been employed together with other force generating mechanisms in devices that provide mechanical motion. Such devices tend to be complex and have construction that do not facilitate miniaturization. Therefore, a new type of motion device that uses shape memory material is needed, that provides for utility and flexibility with low cost and complexity.